The present invention concerns the field of broadcasting digital television programmes and more particularly a method for generating a stream in accordance with the DVB (Digital Video Broadcast) standard that can be decoded by a first-generation decoder, typically in accordance with DVB-S/C/T/, and which also enables the deterministic generation of a stream in accordance with the second-generation DVB-T2 standard.
Historically, the ETSI (European Telecommunications Standards Institute) proposed a first standard, DVB-S, for the broadcasting of programmes by satellite. This standard was developed as the DVB-C standards for broadcasting by cable network and DVB-T for terrestrial broadcasting. These standards will be referred to as first-generation DVB standards.
These standards share a common platform. The programmes are composed of multiplexed audio and video streams to which there is added signalling information in the form of signalling tables known by the term SI/PSI (Service Information/Programme Specific Information) tables. The resulting multiplexed stream is encapsulated in a transport layer in accordance with the standard MPEG-2 TS (Transport Stream) for broadcasting. These standards have experienced clear success and constitute a widespread television broadcasting technology.
At the present time, a new generation of these standards is being developed. In particular, terrestrial broadcasting is standardised in the form of a DVB-T2 standard. This new standard makes it possible to aggregate, in a same stream, several physical layer tunnels referred to as PLPs (Physical Layer Pipes). Each of these physical layer tunnels consists of a multiplex of programs in a transport stream of the MPEG-2 TS (Moving Picture Experts Group 2 Transport Stream) type having its own modulation parameters. These tunnels are collected together in a stream referred to as a T2-MI (Modulator Interface) stream. The T2-MI stream is itself encapsulated in a new layer of the MPTS (Multiple Programme Transport Stream) type. The T2-MI stream comprises T2-MI data packets such as T2-MI timestamp synchronisation packets, signalling packets including the packet called L1-current which gives information on the structure of the T2-MI stream and packets called baseband frames containing the data of the MPEG-2 TS streams of the different various tunnels. The T2-MI packets are organised in a T2-MI frame, each frame contains a T2-MI timestamp packet, an L1-current T2-MI packet and baseband frame packets.
The T2-MI streams are finely synchronised by means of T2-MI timestamp packets so as to enable broadcasting in an SFN (Single Frequency Network) area. These areas consist of a plurality of transmitters broadcasting the same DVB-T2 radio signal on the same frequency. This broadcasting mode is possible only if the transmitters are finely synchronised and the DVB-T2 radio signals transmitted are identical to within a bit, otherwise interference will be generated in the zones covered by the transmissions of at least two transmitters.
The second-generation terrestrial broadcasting standard cannot be adopted by switching and must cohabit with a broadcasting in parallel with the same programmes according to the first-generation standards. If the example is taken of an operator broadcasting a cluster of programmes by satellite according to the DVB-S standard and wishing also to adopt terrestrial broadcasting of the same programmes according to the DVB-T2 standard, it is necessary at the present time to broadcast at least two streams, a first conventional MPEG-2 TS multiplex containing the programmes intended for households provided with a conventional satellite decoder according to the DVB-S standard and a second multiplex comprising T2-MI packets encapsulated in a layer of the MPEG-2 TS type intended for various DVB-T2 transmitters. This gives a duplication of the programmes whereas satellite bandwidth is expensive. These additional costs are a restriction on the development of the DVB-T2 standard second generation.